参数资料
型号: LMV1026UPX
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: 音频/视频放大
英文描述: 1 CHANNEL, AUDIO PREAMPLIFIER, PBGA6
封装: 0.40 MM HEIGHT, LEAD FREE, MO-211CB, MICRO, SMD-6
文件页数: 5/6页
文件大小: 502K
代理商: LMV1026UPX
Application Section
INTERFACE TIMING
For stereo applications, the data is only valid for one half
clock cycle to allow for two microphones on the same I/O
lines (Data and Clock). To avoid overlap between the drivers
of the microphones, one microphone always goes into a high
impedance state before the second microphone starts driv-
ing the line. This is shown in the timing chart below.
TABLE 1. Timing Characteristics
Symbol
Parameter
Typ
Unit
A
Time from rising edge of Clock
to Data becoming high
impedance
50
ns
B
Time from falling edge of
Clock to Data becoming valid.
100
ns
STEREO MICROPHONE
Since the data on the dataline is valid for half a period of the
clock (Figure 1) it is possible to realize an application where
two IC’s communicate over the same I/O lines (Data and
Clock). The LMV1024 and LMV1026 are required to com-
municate in a different half of the clock period. Therefore,
different IC’s have been developed. The LMV1024 is positive
edge triggered and the LMV1026 is negative edge triggered.
When the data of one IC is valid, the data line of the second
IC is high impedance.
This feature enables the realization of a stereo microphone
where two microphones use the same communication lines.
Figure 2 shows the typical application schematic of two
microphones in a stereo application.
LAYOUT CONSIDERATIONS
To obtain the best possible performance of the microphone,
special care needs to be taken for the design of the PCB.
The V
IN trace is the most sensitive as it is connected to the
high impedance electret element. To avoid any switching
noise coupling into the input of the IC, it is essential to isolate
and shield the V
IN trace from the digital signal traces. An
example of an optimized PCB layout is given in Figure 3.
The microphone PCB has two capacitors. One capacitor
(100 nF) is connected to the reference pin of the LMV1024/
LMV1026 and the other (10 nF) is used to decouple high
frequencies from the supply line. No capacitors should be
placed on the data output of the LMV1024/LMV1026 since it
will only load the output driver and degrade the overall
performance. This is contrary to the analog phantom biased
microphones, where capacitors are needed to improve RF
immunity at the output of the device.
20133429
FIGURE 1. Timing Diagram
20133425
FIGURE 2. Stereo Microphone Setup
20133428
FIGURE 3. PCB Layout
LMV1024
/
LMV1026
www.national.com
5
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